The objective of this study is to investigate changes occurring in the peripheral auditory system of premature and fullterm babies during first few months of life on the basis of two types of evoked otoacoustic emissions (EOEs), i.e., distortion-product otoacoustic emissions (DPOEs) and click-evoked otoacoustic emissions (CEOEs). Those changes are expected to arise from maturation and from a variety of medical factors, e.g., treatment with ototoxic drugs. Fifty premature babies of gesta- tional age, 32 weeks or less will be enrolled per year. The first EOE tests will be done as soon as the baby is stable. The tests will be repeated on a weekly basis for as long as the baby stays in the hospital. The Auditory Brainstem Response test will be performed prior to discharging. Follow-up testing will occur at 2 and 4 months corrected age on at least 20 subjects. The EOE data obtained from premature babies will be compared to the EOEs from healthy fullterm babies (30 babies/yr) tested at 2-3 days of age. Follow-up evaluation for at least 20 of those subjects will again be at 2 and 4 months of age. An otoscopic exam will be performed on all babies enrolled in the study prior to EOE evaluation. The Behavioral Observation Audiometry will be done at both follow-up visits. During the second follow-up visit, tympanograms and acoustic reflexes will be measured. The first specific aim of this study is to analyze individual EOE data of each premature baby longitudinally and to correlate observed changes with the age and with a variety of medical factors. The second aim is to compare the EOE data collected from premature babies who have grown to near term status with the EOE baselines of the fullterm newborns and to compare individual EOE data collected at the corrected age of 2 and 4 months from premature babies with the EOE baselines of the fullterm babies of the same age. This analysis will address the question of whether the time course of the developmental changes of the auditory periphery is different for premature babies versus fullterm babies. Data of CEOE and DPOE in premature babies are currently not available in the literature.